EP greases function under highly loaded conditions and require highly effective EP additives to prevent scoring and welding. DMTD derivatives are well known in the art as antiwear and EP additives. Examples of DMTD derivatives that are useful as antiwear additives include mono-sulfide and di-sulfide dimers of DMTD as disclosed in U.S. Pat. Nos. 4,517,103 and 5,194,621, maleate adducts of DMTD as disclosed in U.S. Pat. Nos. 5,102,568, 5,055,584 and 5,138,065 and mono-alkylated and thioacetal derivatives as disclosed in U.S. Pat. No. 5,849,925.
DMTD derivatives are also known to provide exceptional anti-welding properties typically measured by 4-Ball Weld Test (ASTM D-2596). However, these derivatives generally exhibit poor anti-scoring properties typically measured by Timken Load Test (ASTM D-2509).
Complexes of DMTD derivatives with PAG fluids are well-known in the art for providing both anti-scoring and anti-welding properties. Examples of DMTD derivatives used to produce thiadiazole/PAG complexes include mono-sulfide and di-sulfide dimers of DMTD, alkali metal salts of DMTD, half and full ester maleate adducts of DMTD, mono-alkyl, mono-alkyloxy and thioacteal derivatives of DMTD and dimerized DMTD as disclosed in U.S. Pat. Nos. 6,365,557, 6,489,484 and 6,620,771.
Although complexes of DMTD derivatives with PAG fluids are excellent EP additives, they do not provide adequate antiwear to satisfy current performance levels and as per U.S. Patent Application 20090156444, only molybdenum dialkyldithiophosphate was effective in improving the antiwear properties of EP greases formulated with these DMTD complexes. In lieu of the above, there still exists a need in the art for DMTD based additive compositions that provide both robust EP and effective antiwear performance, preferably in the absence of expensive and/or toxic metals such as molybdenum and antimony.